Cooling gas recovered from a well

ABSTRACT

Flow from a gas well is conditioned prior to a production pipeline. A flow line is coupled to a gas well to receive the gas and coupled to a production pipeline to direct the received gas away from the production site, the flow line residing at a production site and comprising an electric power generation system. The electric power generation system has a turbine generator. The inlet nozzle and the turbine wheel of the turbine generator is configured to reduce the pressure and temperature of the received gas to conditions associated with the production pipeline.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation-in-part of and claims the benefit ofpriority to U.S. patent application Ser. No. 17/814,597, filed Jul. 25,2022, the contents of which are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to conditioning gas for a pipeline.

BACKGROUND

Natural gas is one of the principal sources of energy for many of ourday-to-day needs and activities. Natural gas is an attractive fossilfuel for its abundance and relative cleanliness. It is produced fromwells, typically in rural areas, away from national, regional, ormunicipal power grids and other ready sources of electricity. In thecase of subsea natural gas wells, the well production is piped tooffshore platforms far from populated areas. Thus, if electricity isneeded at the production site (including offshore platform) it istypically made on site by burning a portion of the produced gas.

SUMMARY

In certain aspects, a system for conditioning flow from a gas well priorto a production pipeline includes an inlet flow line coupled to awellhead of the gas well to receive gas produced from the gas well. Aflow line is coupled to the inlet flow line to receive the gas and iscoupled to the production pipeline to direct the received gas away froma production site. The flow line resides at the production site andincludes an electric power generation system. The electric powergeneration system includes a turbine wheel configured to receive the gasand rotate in response to expansion of the gas flowing into an inlet ofthe turbine wheel and out of an outlet of the turbine wheel. A nozzle isconfigured to direct gas into the inlet of the turbine wheel. Anelectric rotor is coupled to the turbine wheel and configured to rotatewith the turbine wheel within a stationary electric stator. The electricrotor and electric stator defining an electric generator configured togenerate current upon rotation of the electric rotor within the electricstator. In certain instances, the turbine wheel is configured to reducethe temperature of the received gas at an inlet to the productionpipeline to at least a specified temperature associated with theproduction pipeline. In certain instances, the turbine wheel can beconfigured to have an isentropic efficiency of 80% or lower at theconditions of the received gas.

In certain aspects, a method of conditioning a flow from a gas well fora production pipeline includes receiving flow from the gas well at aflow line. The flow line includes an electric power generation systemresiding on a production site of the well. The flow line includes aturbine wheel configured to receive the gas and rotate in response toexpansion of the gas flowing into an inlet of the turbine wheel and outof an outlet of the turbine wheel. It also includes a nozzle configuredto direct gas to the inlet of the turbine wheel. An electric rotor iscoupled to the turbine wheel and configured to rotate with the turbinewheel within a stationary electric stator. The electric rotor andelectric stator define an electric generator configured to generatecurrent upon rotation of the electric rotor within the electric stator.In certain instances, a portion of the flow from the gas well is flowedthrough the flow line and the electric power generation system and, withthe turbine, the temperature of the gas is reduced at an inlet to theproduction pipeline to at least a specified temperature associated withthe production pipeline. In certain instances, a portion of the flowfrom the gas well is flowed through the flow line and the electric powergeneration system, with the turbine operating at an isentropicefficiency of 80% or lower.

In certain aspects, a system includes a flow path from a well to apipeline having a nozzle and a turbine wheel coupled to a generatorresiding on a production site of the well. The nozzle and the turbinewheel are configured to reduce the temperature of gas received throughthe flow path to at least a specified temperature associated with thepipeline. In certain instances, the nozzle and the turbine wheel areconfigured to reduce the temperature of gas received through the flowpath to no lower than a specified minimum temperature associated withthe pipeline while operating at an isentropic efficiency of 80% or less.

The aspects above include some, all or none of the following features.

In certain instances, the turbine wheel is configured to have anisentropic efficiency of 80% or lower when both (i) reducing thepressure of the received gas, at an inlet to the production pipeline, toat least a specified maximum pressure associated with the pipeline and(ii) reducing the temperature of the received gas, at the inlet to theproduction pipeline, to no lower than a specified minimum temperatureassociated with the pipeline.

The isentropic efficiency of the turbine wheel can be selected based onthe conditions of the received gas, the specified maximum pressure andthe specified minimum temperature.

The turbine wheel can be configured to reduce the temperature of thereceived gas from a temperature higher than a specified maximumtemperature associated with the pipeline to a temperature lower than thespecified maximum temperature.

The nozzle and the turbine wheel can be configured to reduce thetemperature of the received gas to no lower than a temperature at whichhydrates form in the gas at an inlet of the pipeline.

In certain instances, the nozzle and the turbine wheel are configured toreduce the temperature of the received gas to 38° C. or lower.

The flow path between the turbine wheel and production pipeline can beprovided without a heater.

The nozzle and the turbine wheel characteristics can be selected basedon the specified minimum temperature of the pipeline to be above thespecified minimum temperature over the operating life of the well.

A hermetically sealed housing can enclose the turbine wheel, theelectric rotor and the electric stator and be hermetically sealed inlinein the first mentioned flow line so that received flow flows through theturbine and over the electric stator.

A flow control valve can be provided in the flow line upstream of theelectric power generation system.

In certain instances, a second flow line is coupled to the inlet flowline to receive the gas and provide an alternate flow path for the gasaround the first mentioned flow line. The second flow line includes apressure control valve, and the first mentioned flow line and the secondflow line are coupled downstream of the electric power generation systemto recombine flow from the first mentioned flow line and the second flowline. In certain instances, the nozzle and the turbine wheel areconfigured to, in cooperation with the pressure control valve in thesecond flow line, maintain a temperature of the received gas at an inletto the production pipeline to be above a specified minimum temperatureassociated with the production pipeline while the well is producing gasabove a specified maximum pressure associated with the productionpipeline. The nozzle and turbine wheel can be configured to, incooperation with the pressure control valve in the second flow line,maintain a pressure of the received gas at the inlet to the productionpipeline to be below the specified maximum pressure associated with theproduction pipeline. In certain instances, the nozzle and the turbinewheel characteristics are selected to maximize the amount of powerproduced by the electric power generation system while, in cooperationwith the pressure control valve in the second flow line, maintaining atemperature of the received gas at an inlet to the production pipelineabove the specified minimum temperature while the well is producing gasabove a specified maximum pressure associated with the productionpipeline.

The details of one or more implementations of the subject matterdescribed in this disclosure are set forth in the accompanying drawingsand the description below. Other features, aspects, and advantages ofthe subject matter will become apparent from the description, thedrawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electric power generation system inaccordance with the concepts herein.

FIG. 2 is a schematic diagram of an example turboexpander system inaccordance with the concepts herein.

FIG. 3 is a schematic diagram of an example energy recovery system withan electric power generation system in accordance with the conceptsherein.

FIG. 4 is a schematic diagram of another example energy recovery systemwith two electric power generation systems in accordance with theconcepts herein.

Like reference symbols in the various drawings indicate like elements.The drawings are not to scale.

DETAILED DESCRIPTION

Natural gas wells produce at high pressure and temperature, sometimes asmuch as 9,000 PSIG (62.05 MPa) or even 15,000 PSIG (103.42 MPa) and attemperatures over 100° F. (38° C.) or even 150° F. (66° C.) and hotter.The pressure of the produced natural gas must be reduced prior topre-processing, which separates particulates and moisture from the gas,and for transport via pipeline. Likewise, the temperature of the gasmust be reduced to the operating temperature of the pipelines. Thepipelines, for example, transport gasses from production sites (e.g.,well sites) to processing facilities and from processing facilities tolocal distribution networks, such as regional, city or district networksor on site industrial plants networks.

The processes at the production sites and intermediate pressure letdownstations use pressure control valves (i.e., choke or throttle valves) toachieve the required pressure drops, but also waste significant amountsof head pressure energy in the process. Additional pressure controlvalves can be used at other locations for pressure control within thesub-processes of the processing facilities and within the end user'sprocesses and piping. A chiller, and typically multiple chillers, areoften used upstream of the pipeline (e.g., at the production site) toreduce the temperature of the gas produced to the operating temperatureof the pipeline. Typical chillers include vapor-compression cycle typechillers and absorption chillers. In any case, the chillers consumepower, and are often powered by a portion of the produced natural gas.

An energy recovery system, according to the concepts herein, can be usedin lieu of or in combination with one or more of the above-mentionedpressure control valves to both control the pressure of the gas providedto the pipeline to the operating pressure of the pipeline and to reduceits temperature to the operating temperature of the pipeline. Use ofsuch an energy recovery system can cool the gas, enabling eliminating orreducing the number of chillers (and associated power consumption)required to cool the gas for the pipeline. The energy recovery systemcan reside at the production site and/or elsewhere (e.g., at theintermediate pressure letdown station and other locations where thepressure control valves are used). The system includes a turboexpander(with a generator) that can be installed in-line in a flow line from thewellhead, often in parallel to a bypass flow line with a pressurecontrol valve, to extract the wasted energy from pressure andtemperature reduction and produce electrical power. The electrical powercan be directed to a power grid or elsewhere. For example, some or allof the power can be used at the production site (onshore or offshore) tosupply or offset the site's power needs, such as powering equipment atthe production site. Some production sites, especially offshoreplatforms, have no other source of electric power than that made on site(e.g., by running natural gas powered generators off the produced gas orby diesel fueled generators). Thus, the energy recovery system can bringpower to production sites and other remote locations without burning theproduced gas and the resultant emissions. In each instance, byrecovering lost energy from produced natural gas, the energy recoverysystem can generate electricity while also reducing CO2 emissions,increasing overall plant efficiency, offsetting electrical costs, andgenerating additional revenue.

FIG. 1 is a schematic diagram of an electric power generation system 100coupled to a power grid 140 in accordance with embodiments of thepresent disclosure. As discussed in more detail below, the grid 140 maybe a municipal grid, a microgrid, or the system 100 may be directlycoupled to one or more pieces of equipment powered by its output. Theelectric power generation system 100 includes a turboexpander 102 inparallel with a pressure control valve 130. The turboexpander 102 isarranged axially so that the turboexpander 102 can be mounted in-linewith a pipe. The turboexpander 102 acts as an electric generator byconverting kinetic energy to rotational energy from gas expansionthrough a turbine wheel 104 and generating electrical energy. Forexample, rotation of the turbine wheel 104 can be used to rotate a rotor108 within a stator 110, which then generates electrical energy.

The turboexpander 102 includes a high-performance, high-speed permanentmagnet generator with an integrated radial in-flow expansion turbinewheel 104 and low loss active magnetic bearings (AMBs) 116 a,b. Therotor assembly consists of the permanent magnet section with the turbinewheel 104 mounted directly to the rotor hub. The rotor 108 is levitatedby the magnetic bearing system creating a frictionless (or nearfrictionless) interface between dynamic and static components. The AMBs116 a,b facilitate a lossless (or near lossless) rotation of the rotor108.

The turboexpander 102 includes a high-performance, high-speed permanentmagnet generator with an integrated radial in-flow expansion turbinewheel 104 and low loss active magnetic bearings (AMBs) 116 a,b. Therotor assembly includes the permanent magnet section with the turbinewheel 104 mounted directly to the rotor hub of the rotor 108. The rotor108 is levitated by the magnetic bearing system, for example, atlongitudinal ends (e.g., axial ends) of the rotor 108, creating africtionless (or near frictionless) interface between dynamic and staticcomponents. The AMBs 116 a,b facilitate a lossless (or near lossless)rotation of the rotor 108.

The turboexpander 102 is designed to have process gas flow through thesystem, which cools the generator section and eliminates the need forauxiliary cooling equipment. The power electronics 118 for theturboexpander 102 combines a Variable Speed Drive (VSD) 206 and MagneticBearing Controller (MBC) 212 into one cabinet, in some implementations.The VSD allows for a consistent and clean delivery of generated powerfrom the turboexpander 102 to a power grid 140. For example, the VSD 206regulates the frequency and/or amplitude of the generated current tomatch the grid and/or power requirements of its load. After expansion,the gas exits the turboexpander 102 along the same axial path fordownstream processes.

The turboexpander 102 includes a flow-through configuration. Theflow-through configuration permits process gas to flow from an inletside of the turboexpander 102 to an outlet side of the turboexpander102, where the inlet and outlet are centered on the same axis.Internally, the gas flows into a gas inlet nozzle 154 to a turbine wheel104 and an axial gas outlet 156 from the turbine wheel 104. The gas thenflows through the generator and out of the outlet 152, where the gasrejoins the gas pipeline 170. Generally, high pressure process gas 120,e.g. from a natural gas well, is directed to flow into the turboexpander102 through a flow control system 126. The flow control system 126includes a flow or mass control valve and an emergency shut off valve.In embodiments, the turboexpander housing 112 is hermetically sealed.

The high pressure process gas 120 is expanded by flowing through theturbine wheel 104, resulting in a pressure letdown of the process gas.Lower pressure process gas 128 exits the turboexpander 102. Theexpansion of the high pressure process gas 120 through the turbine wheel104 causes the turbine wheel 104 to rotate, which causes the rotor 108to rotate. The rotation of the rotor 108 within the stator 110 generateselectrical energy. The turboexpander 102 achieves the desired pressureletdown and captures the energy from the pressure letdown to generateelectricity. A pressure control valve 130, such as a conventional choke,can be installed in parallel to the turboexpander 102. The pressurecontrol valve 130 can be used to control the pressure of the highpressure process gas 120 that flows in parallel to the turboexpander102. Any excess high pressure process gas that is not directed into theturboexpander can be directed through the pressure control valve 130.

As the gas is expanded through the turbine wheel 104 it is cooled. Thatgas then flows through the electrical portion of the turboexpander 102,thus cooling the generator components (e.g., rotor 108, stator 110, andother components). Cooling the generator components also supplies heatto the gas flow exiting the turboexpander 102. In some embodiments, aheater 122 can heat the high pressure process gas 120 prior to flowingthe gas into the turboexpander 102. For example, if the expansion of thegas through the turbine wheel 104 would lower the temperature of theprocess gas to a point where moisture in the gas freezes and/or processgas components condense at, or downstream of, the turbine wheel or atother downstream locations in the pipeline, the pressurized process gas120 can be heated by heater 122 prior to flowing through theturboexpander 102. Heated high pressure process gas 124 can then bedirected into the turboexpander 102. The heating of the process gas canprevent freezing moisture or component condensation as the gas expandsand its temperature drops.

The turboexpander 102 includes a stationary aerodynamic stator. Theaerodynamic stator is shown as the stationary components defining nozzle154. Although shown converging to radial at the inlet of the turbinewheel 104, other configurations are within the scope of this disclosure,such as a nozzle converging to slanted or a curved shape. The nozzle 154increases the gas velocity and directs the gas onto the turbine wheel104 at a given angle. Both magnitude and direction of gas exiting fromthe nozzle 154 have an effect on the level of power generation. Thenozzle 154 can, in certain instances, have multiple blades therethrough.The gas velocity exiting the nozzle 154 can be adjusted by selecting thenumber of blades, blade height and blade profile.

The turboexpander 102 includes a turbine wheel 104. The turbine wheel104 is shown as a radial inflow turbine wheel, though otherconfigurations are within the scope of this disclosure, such as an axialflow turbine. In this example, heated high pressure process gas 124 isreceived from an inlet conduit 150 of the housing 112 enters a nozzle154 of the turbine wheel 104. In certain embodiments, the fluid flowsthrough an inlet conduit 150 and is diverted by a flow diverter 158 to anozzle 154 that directs the flow into the radial inflow of the turbinewheel 104. In the example turboexpander 102 of FIG. 1 , the flowdiverter 158 includes a cone-shaped nose that diverts the gas flowradially outward to the nozzle 154. The flow diverter 158 can beconnected to or integrally formed with the bearing 116 a and sensor 117a at the inlet side of the turboexpander 102 and the supports for thisbearing 116 a and sensor 117 a surrounding the axial end of the rotor108 at the inlet end of the turboexpander 102. After expanding, thelower pressure process gas exits the turbine wheel 104 from an axiallyoriented outlet 156 to outlet conduit 152 of the housing 112 at theoutlet end of the turboexpander 102.

The turbine wheel 104 can be directly affixed to the rotor 108, or to anintermediate common shaft, for example, by fasteners, rigid drive shaft,welding, or other manner. For example, the turbine wheel 104 may bereceived at an axial end of the rotor 108, and held to the rotor 108with a shaft. The shaft threads into the rotor 108 at one end, and atthe other end, captures the turbine wheel 104 between the end of rotor108 and a nut threaded on the shaft. The turbine wheel 104 and rotor 108can be coupled without a gearbox and rotate at the same speed. In otherinstances, the turbine wheel 104 can be indirectly coupled to the rotor108, for example, by a gear train, clutch mechanism, or other manner.

The turbine wheel 104 includes a plurality of turbine wheel blades 106extending outwardly from a hub and that react with the expanding processgas to cause the turbine wheel 104 to rotate. FIG. 1 shows an unshroudedturbine wheel, in which each of the turbine blades 106 has an exposed,generally radially oriented blade tip extending between the nozzle 154and axial outlet 156. As discussed in more detail below, the blade tipssubstantially seal against a shroud 114 on the interior of the housing112. In certain instances, the turbine wheel 104 is a shrouded turbinewheel.

In configurations with an un-shrouded turbine wheel 104, the housing 112includes an inwardly oriented shroud 114 that resides closely adjacentto, and at most times during operation, out of contact with the turbinewheel blades 106. The close proximity of the turbine wheel blades 106and shroud 114 substantially seals against passage of process gastherebetween, as the process gas flows through the turbine wheel 104.Although some amount of the process gas may leak or pass between theturbine wheel blades 106 and the shroud 114, the leakage isinsubstantial in the operation of the turbine wheel 104. In certaininstances, the leakage can be commensurate with other similarunshrouded-turbine/shroud-surface interfaces, using conventionaltolerances between the turbine wheel blades 106 and the shroud 114. Theamount of leakage that is considered acceptable leakage may bepredetermined. The operational parameters of the turboexpander may beoptimized to reduce the leakage. In embodiments, the housing 112 ishermetically sealed to prevent process gases from escaping the nozzle154 of the turbine wheel 104.

The shroud 114 may reside at a specified distance away from the turbinewheel blades 106, and the turbine wheel 104 position is controlled tomaintain the shroud 114 at a specified distance away from the turbinewheel blades 106 during operation of the turboexpander 102 by usingmagnetic positioning devices, including active magnetic bearings andposition sensors.

As mentioned above, the turboexpander 102 generates rotational motionfrom gas expansion through the turbine wheel 104, which in turn, reducesthe pressure and temperature of the process gas 120 expelled at theoutlet of the turbine wheel 104. The structures defining the nozzle 154and the shroud 114 (collectively the aerodynamic stator), the turbinewheel 104, the aerodynamic characteristics of the surfaces leading up tothe turbine wheel 104, and the aerodynamics of the other flow passagesthrough the turboexpander 102 can be tuned based on inlet temperature,pressure and composition to control characteristics such as the power(rotational speed and/or torque) generated by the wheel and the pressureand/or temperature output from the turbine wheel 104. In other words,the configuration of the aerodynamic stator, the turbine wheel 104 andother surfaces can be used analogously to a process control device tomeet pressure and temperature specifications downstream of theturboexpander 102, as well as other characteristics like dew point.Moreover, the aerodynamic stator, the turbine wheel 104 and othersurfaces can be customized aerodynamically, without substantiallyaffecting other configuration aspects of the turboexpander 102.

The turbine wheel 104 can be tuned by selecting the diameter of theturbine wheel, the shape and number of blades, the surface finish of theaerodynamic surfaces of the wheel (e.g., the blades and interstitialsurfaces), whether the wheel is shrouded, and if shrouded the shroudshape, and, if unshrouded, the position of the blades relative to theshroud. The shroud 114 and inlet surfaces leading up to the turbinewheel 104 can be tuned by selecting the distance between the shroud 114and blades of the turbine wheel 114 and shaping the effective nozzlecreated by the surfaces leading up to the turbine wheel 104 and shroud114. The wheel, shroud and surfaces can be modeled using computationalfluid dynamics (CFD) software and iteratively adjusted to achieve thedesired characteristics, then constructed and tested, and if necessary,iteratively adjusted in CFD, constructed and tested one or moreadditional times, to produce the desired characteristics. For example,the aerodynamic stator, the turbine wheel 104, and the other aerodynamicpathways through the turboexpander 102 can be designed to prioritize thepower produced by the turbine wheel 104, prioritize the pressurecharacteristics at the outlet of the turbine wheel 104 (andturboexpander housing 112), prioritize the temperature characteristicsat the outlet of the turbine wheel 104 (and housing 112) and/orprioritize or balance one or more of these characteristics. In certaininstances, the aerodynamic stator, the turbine wheel 104 and othersurfaces can be configured to target specific isenthalpic efficienciesand isentropic efficiencies to control the outlet conditions of theturboexpander 102 relative to the gas supplied, and the desired powergeneration.

Bearings 116 a and 116 b are arranged to rotatably support the rotor 108and turbine wheel 104 relative to the stator 110 and the shroud 114. Theturbine wheel 104 is supported by the bearings 116 a and 116 b. Inembodiments, the turbine wheel 104 may be supported in a cantileveredmanner and bearings 116 a and 116 b may be located on one side ofturbine wheel 104. In certain instances, one or more of the bearings 116a or 116 b can include ball bearings, needle bearings, magneticbearings, foil bearings, journal bearings, or other bearing types.

Bearings 116 a and 116 b may be a combination radial and thrust bearing,supporting the rotor 108 in radial and axial directions. Otherconfigurations could be utilized. The bearings 116 a and 116 b need notbe the same types of bearings.

In the embodiments in which the bearings 116 a and 116 b are magneticbearings, a magnetic bearing controller (MBC) 212 is used to control themagnetic bearings 116 a and 116 b. Position sensors 117 a, 117 b can beused to detect the position or changes in the position of the turbinewheel 104 and/or rotor 108 relative to the housing 112 or otherreference point (such as a predetermined value). Position sensors 117 a,117 b are connected to the housing 112 directly or indirectly, and theposition sensors 117 a, 117 b can detect axial and/or radialdisplacement of the rotor 108 and its connected components (e.g.,turbine wheel 104) relative to the housing 112. The magnetic bearing 116a and/or 116 b can respond to the information from the positions sensors117 a, 117 b and adjust for the detected displacement, if necessary. TheMBC 212 may receive information from the position sensor(s) 117 a, 117 band process that information to provide control signals to the magneticbearings 116 a, 116 b. MBC 212 can communicate with the variouscomponents of the turboexpander 102 across a communications channel 162.

The use of magnetic bearings 116 a, 116 b and position sensors 117 a,117 b to maintain and/or adjust the position of the turbine wheel blades106 such that the turbine wheel blades 106 stay in close proximity tothe shroud 114 permits the turboexpander 102 to operate without the needfor seals (e.g., without the need for dynamic seals). The use of theactive magnetic bearings 116 a,b in the turboexpander 102 eliminatesphysical contact between rotating and stationary components, as well asthe need for lubrication, lubrication systems, and bearing seals. Insome instances, brush, labyrinth or other types of seals are used onboth sides of the rotor 106 to help balance the axial thrust load.

The turboexpander 102 may include one or more backup bearings. Forexample, in the event of a power outage that affects the operation ofthe magnetic bearings 116 a and 116 b, bearings may be used to rotatablysupport the turbine wheel 104 during that period of time. The backupbearings may include ball bearings, needle bearings, journal bearings,or the like.

As mentioned previously, the turboexpander 102 is configured to generateelectricity in response to the rotation of the rotor 108. In certaininstances, the rotor 108 can include one or more permanent magnetscoupled to the rotor 108, for example, on a radially outer surface ofthe rotor 108 adjacent to the stator 110. The stator 110 includes aplurality of conductive coils, for example, positioned adjacent to themagnet(s) on the rotor 108. Electrical current is generated by therotation of the magnet(s) within the coils of the stator 110. The rotor108 and stator 110 can be configured as a synchronous, permanent magnet,multiphase alternating current (AC) generator. The electrical output 160can be a three-phase output, for example. In certain instances, stator110 may include a plurality of coils (e.g., three or six coils for athree-phase AC output). When the rotor 108 is rotated, a voltage isinduced in the stator coil. At any instant, the magnitude of the voltageinduced in the coils is proportional to the rate at which the magneticfield encircled by the coil is changing with time (i.e., the rate atwhich the magnetic field is passing the two sides of the coil). Ininstances where the rotor 108 is coupled to rotate at the same speed asthe turbine wheel 104, the turboexpander 102 is configured to generateelectricity at that speed. Such a turboexpander 102 is what is referredto as a “high speed” turbine generator. For example, in embodiments, theturboexpander 102 can produce up to 135 kilowatts (kW) of power at acontinuous speed of 25,000 revolutions per minute (rpm) of the rotor108. In embodiments, the turboexpander 102 can produce on the order of315 kW at certain rotational speeds (e.g., on the order of 23,000 rpm).

In some embodiments, the design of the turbine wheel 104, rotor 108,and/or stator 110 can be based on a desired parameter of the output gasfrom the turboexpander 102. For example, the design of the rotor 108 andstator 110 can be based on an expected or desired pressure and/ortemperature of the gas 128 at the input of the turboexpander 102, outputof the turboexpander 102, or both.

In the example system 100 of FIG. 1 , the turboexpander 102 is coupledto power electronics 118. Power electronics 118 includes the variablespeed drive (VSD) 206 (or variable frequency drive) and the magneticbearing controller (MBC) 212 (discussed above).

The electrical output 160 of the turboexpander 102 is connected to theVSD 206, which can be programmed to specific power requirements. The VSD206 can include an insulated-gate bipolar transistor (IGBT) rectifier208 to convert the variable frequency, high voltage output from theturboexpander 102 to a direct current (DC). The rectifier 208 can be athree-phase rectifier for three-phase AC input current. An inverter 210then converts the DC from the rectifier AC for supplying to the powergrid 140 (or other load). The inverter 210 can convert the DC to 380VAC-480 VAC at 50 to 60 Hz for delivery to the power grid. The specificoutput of the VSD 206 depends on the power grid and application. Otherconversion values are within the scope of this disclosure. The VSD 206matches its output to the power grid 140 by sampling the grid voltageand frequency, and then changing the output voltage and frequency of theinverter 210 to match the sampled power grid voltage and frequency.

The turboexpander 102 is also connected to the MBC 212 in the powerelectronics 118. The MBC 212 constantly monitors position, current,temperature, and other parameters to ensure that the turboexpander 102and the active magnetic bearings 116 a and 116 b are operating asdesired. For example, the MBC 212 is coupled to position sensors 117 a,117 b to monitor radial and/or axial position of the turbine wheel 104and the rotor 108. The MBC 212 can control the magnetic bearings 116 a,116 b to selectively change the stiffness and damping characteristics ofthe magnetic bearings 116 a, 116 b as a function of spin speed. The MBC212 can also control synchronous cancellation, including automaticbalancing control, adaptive vibration control, adaptive vibrationrejection, and unbalance force rejection control.

FIG. 2 is a schematic diagram of an example turboexpander system 200that includes a brake resistor assembly 202 in accordance withembodiments of the present disclosure. Turboexpander system 200 includesa turboexpander 102 and a power electronics 118. The turboexpander 102receives a heated high pressure process gas 124, which causes a turbinewheel 104 to rotate. The rotation of the turbine wheel 104 rotates arotor 108 that supports a plurality of permanent magnets. The rotationof the permanent magnets on the rotor 108 induces a current throughcoils or windings on stator 110.

The electric generator system acts as a brake on the rotor 108. Thisbraking torque converts the shaft power, created by the process gasflow, to electrical power that can be put on an electrical grid, forexample. In the case of a grid or load failure, inverter failure, orother fault condition, braking torque is lost and the rotor 108 may spinup towards an undesirable over speed. To prevent over speed, the powercan be diverted to a brake resistor assembly 202 that can temporarilyabsorb the electricity until the process gas flow is reduced or removed(e.g., by flow control system 126) or until the fault condition isresolved. Flow control system 126 can include a one or a combination ofa flow control valve or a mass control valve or an emergency shutoffvalve. Flow control system 126 can be controlled by power electronics118 or other electrical, mechanical, or electromagnetic signal. Forexample, a fault condition can signal the flow control system 126 toclose or partially close, thereby removing or restricting gas supply tothe turboexpander 102. Restricting or removing gas flow to theturboexpander reduces the shaft power developed by the turbine wheel andconsequently, slows the rotor. In the example shown in FIGS. 1 and 2 , asignal channel 164 from the power electronics 118 can be used to openand/or close the flow control system 126.

A fault condition can include a grid or load failure, VSD failure,inverter failure, or other fault condition. A fault condition caninclude any condition that removes or reduces the braking torque on therotor 108.

A brake resistor assembly 202 is electrically connected to theelectrical output 160 of the turboexpander 102 (e.g., the output of thegenerator). The brake resistor assembly 202 can have a tuned impedanceto allow an efficient transfer of power from the turboexpander 102 tothe brake resistor assembly 202.

In embodiments, a contactor 204 can connect the output current of theturboexpander 102 to the brake resistor assembly 202 when there is afault condition at the VSD 206 or the power grid 140. The contactor 204is an electrically controlled switch for switching in an electricalpower circuit. The contactor 204 can accommodate the three-phase currentoutput from the generator to direct the current to the brake resistorassembly 202.

In some embodiments, the contactor 204 is connected directly to the(three-phase) electrical output 160 of the turboexpander 102. In someembodiments, the brake resistor assembly 202 and/or the contactor 204are not part of the power electronics, but are connected to theelectrical output 160 of the turboexpander 102 outside of the powerelectronics 118.

The VSD 206 can provide an energizing signal 220 to the coil of thecontactor 204 to cause the contactor 204 to connect the electricaloutput 160 of the turboexpander to the brake resistor assembly 202.Depending on the implementation choice, the contactor 204 can be anormally closed (NC) contactor or a normally open (NO) contactor.

For example, in an example implementation using a NO contactor, duringnormal operating conditions, the electrical output 160 of theturboexpander 102 is connected to the VSD 206 and supplies three-phaseAC current to the VSD 206. In a fault condition, the VSD can energizethe contactor 204 to connect the contactor 204 to the electrical output160 of the turboexpander 102. In some implementations, the energizingsignal 220 to the contactor 204 can be provided by another source thatcan respond to a fault condition (e.g., another component of the powerelectronics 118 or another component outside the power electronics 118).In this implementation, if failure of the VSD 206 is the cause of thefault condition, the contactor 204 can operate independent of the VSD206.

If an NC contactor is used, then the VSD 206 (or other source) providesan energizing signal 220 to the contactor 204 to keep the contactorswitches open during normal operating conditions. A fault condition canresult in the removal of the energizing signal 220 to the contactor 204,which results in the contactor switches closing and completing thecircuit between the electrical output 160 of the turboexpander 102 andthe brake resistor assembly 202.

FIG. 3 shows an example energy recovery system 300 coupled to andbetween a wellhead 302 of a well 304 and a production pipeline 320. Theproduction pipeline 320 is the pipeline that communicates the producedfluids from the well 304 to one or more processing facilities (not show)and ultimately on to the end user. The system 300 includes an electricpower generation system 350, with a turboexpander 102 (with generator),for recovering energy from reducing the pressure of the produced fluidsfrom the well 304, as well as associated flow lines and other equipment.In certain instances, the system 300 resides at the production site 312,in proximity to the wellhead 302. In certain instances, the system 300resides on or off the production site 312, upstream of the productionpipeline 320. In one example of a land based well 304, the productionsite 312 is, and the system 300 resides on, the site with the other nearwell 304 equipment, upstream of the production pipeline 320. In anotherexample, multiple land based wells 304 are on the same production site312 feeding to the same pipeline 320, and the system 300 is coupled toone or more of the wells 304 and resides on the site 312. In certaininstances, a production site can be half an acre (2,000 square meters)to two acres (8,000 square meters) in surface area. In one example of asubsea well 304, the production site 312 is, and system 300 resides on,a platform at the ocean surface. The platform can be a productionplatform corresponding to the well 304 (i.e., a subsea well), or it canbe at a production platform associated with multiple of subsea wells304, for example, where the wells 304 are manifolded to flow to a singleproduction platform. In certain instances, the system 300 can reside ona dedicated platform apart from any production platform, and be coupledby a flow line to one or more other production platforms.

In certain instances, the electric power generation system 350 is thesame as the electric power generation system 100. With reference toFIGS. 1 and 2 , the system 350 includes, among other things of system100, the above described turboexpander 102 in a hermetic housing 112,the electrical output of the generator of the turboexpander 102 beingcoupled to power electronics 118, including a VSD 206 with, in someinstances, a brake resistor assembly 202. The turboexpander 102 can beconfigured to handle the gas conditions produced by the well 304, forexample, configured to handle a specified amount of liquid in the gas,particulate in the gas, as well as to be resistant to corrosive aspects(e.g., hydrogen sulfide) in the gas. In certain instances, the VSD 206can be coupled to a cooling system 352 to cool the electronics of theVSD 206 to maintain temperatures below a specified operatingtemperature. The output of the VSD 206 can be electrically coupled to aload 354, such as a power grid to supply power to the grid, as describedabove, a microgrid at the production site 312 for supplying power toequipment used for producing or treating gas at the production site 312,and/or directly to one or more pieces of equipment used for producing ortreating gas at the production site 312 to supply power to theequipment. In certain instances, the equipment includes flow, pressure,temperature, and level sensors of various equipment, valve actuators,communications equipment for allowing remote communication with thesensors, other equipment and control of the valve actuators, separators(e.g., sand separators, liquid separators), heater treaters, sitelighting, control trailers and/or other types of equipment. In certaininstances, the electricity produced by the electric power generationsystem 350 can be used by other equipment at the production site 312 notinvolved in producing or treating the gas from the well 304. Forexample, the electricity can be used to power a hydrogen electrolyzer ina process on the production site 312 for producing hydrogen from thewater.

The system 300 includes an inlet flow line 310 coupled to an outlet ofthe wellhead 302. Well production, that is primarily gaseous natural gas(but often also has some oil, water, moisture, and particulate), flowsfrom the wellhead 302, and flows through flow line 310. The flow line310 includes flow conditioning equipment to condition the flow tospecified conditions selected based on the specification of pipeline 320and equipment downstream of the production site 312, as well as based onthe characteristics of the turboexpander 102 of the electric powergeneration system 350. In FIG. 3 the conditioning equipment is shown asa solids and liquids separator 306 and a dryer 308, but the conditioningequipment could include additional, different or fewer pieces and typesof equipment. For example, the conditioning equipment can includeseparators, molecular dries, knock-out drums, two-phase coalescersand/or other types of conditioning equipment. Turning back to thespecific example of FIG. 3 , flow in flow line 310 flows from thewellhead 302 to and through the separator 306. In the separator 306,solids and liquids are separated from the gaseous flow. Thereafter, theflow flows through the flow line 310 to the dryer 308, where it is driedto reduce moisture in the flow to a specified level selected (in part orentirely) based on the specification of the turboexpander 102 of theelectric power generation system 350. From the dryer 308, the flow flowsthrough the flow line 310 to a pressure control valve 314. The pressurecontrol valve 314 can be controlled to reduce the pressure of the gasflow to a specified pressure. Each of the valves herein, whether controlor isolation or other, can be remote controlled, e.g., via an operatorat a remote control board on the production site 312 or elsewhere orboth, and/or autonomously controlled by a control algorithm of acontroller residing at the production site 312 or elsewhere or both.

In the configuration of FIG. 3 , flow from the pressure control valve314 is split into a first downstream flow line 316 that includes anelectric power generation system 350, including a turboexpander 102, anda second downstream flow line 318 that provides an alternate flow patharound, i.e., bypasses, the turboexpander 102. The first downstream flowline 316 and second downstream flow line 318 recombine upstream of theproduction pipeline 320 and the remaining portion of the flow line 310is coupled to the inlet of the production pipeline 320. In otherinstances, the second downstream flow line 318 can be omitted and theonly path to the production pipeline 320 is through the electric powergeneration system 350. Flow into the production pipeline 320 leaves theproduction site 312. The inlet of the hermetic housing 112 ishermetically coupled in-line with first flow line 316 so that all fluidin the flow line 316 is directed into the hermetic housing 112, flowsthrough the housing 112, and back into the remainder of first flow line316. Often, a production pipeline (e.g., pipeline 320) will have beenprovided by and maintained by a different entity, a production pipelineoperator, than that providing and maintaining the equipment at theproduction site.

When provided, the second flow line 318 includes a pressure controlvalve 322 (e.g., pressure control valve 130) configured with a specifiedpressure drop to actuation position correlation. The pressure controlvalve 322 can be controlled to regulate the pressure in the second flowline 318 downstream of the valve 322, and in turn (as a function of thepressure of the flow coming from the well) the pressure upstream of thepressure control valve 322 and the pressure in the first flow line 316.The first flow line 316 includes a flow control valve 324 (e.g., flowcontrol valve 126), configured with a specified flow rate to actuationposition correlation. The flow control valve 324 can be controlled inrelation to the pressure control valves 314, 322 to control the flowrate of fluid flowing through the first flow line 316, and thus the flowrate of flowing through the turboexpander 102.

This arrangement provides the turboexpander 102 in parallel to thesecond flow line 318, and as will be discussed in more detail below,allows freedom in sizing the turboexpander 102 relative to the pressureand flow rate of flow produced from the well 304 as well as relative tothe conditions of the pipeline 320. The freedom stems, in part, from thesecond flow line 318 allowing flow to selectively bypass theturboexpander 102 in flowing from the wellhead 302 to the productionpipeline 320. In short, however, all flow need not pass through theturboexpander 102 in flowing from the wellhead 302 to the pipeline 320,so the turboexpander 102 need not be sized to receive all of the flow.The first flow line 316 also includes an emergency shut-off valve 326upstream of the turboexpander 102 to quickly shut off flow to theturboexpander 102, if needed. When closed, the entirety of the flowflows through the second flow line 318. Notably, although not shown, theinlet flow line 310, first flow line 316 and second flow line 318 canadditionally be instrumented with sensors to monitor the pressure,temperature, flow rate, and/or other characteristics of the flow in eachline and upstream and/or downstream of each component (e.g., valves,turboexpander and other components in the flow lines).

In operation, when the well 304 is new and first put on production, thefluids produced from the well 304 are at or near their highest pressureand flow rate. Over the operating life of the well 304, the pressure ofthe produced fluids declines, as does the flow rate of the producedfluids until the well is no longer viable to operate. Thus, pressure ofthe production flow is regulated with the pressure control valve 314 inthe flow line 310 to a specified pressure. The pressure control valve322 in the second flow line 318 is, in turn, controlled to maintain thepressure through the first flow line 316 and through the turboexpander102 so that together with the flow control valve 324 the conditionsthrough the turboexpander 102 are maintained within the turboexpander'sspecified operating range. Excess flow exits the second flow line 318and is directed to the pipeline 320. The flow through the first flowline 316 flows through the turboexpander 102, generating power, and thenback to recombine with the flow from the second flow line 318 and on tothe pipeline 320.

The characteristics of the turboexpander 102, including its turbinewheel 104 and other aerodynamic flow passages through the turboexpander102, are selected based on a number of factors, including the expectedpressures, temperatures and flow rates that can be maintained by thewell 304 over time, the timeframe during the operating life of the well304 that power generated by the turboexpander 102 is desired or needed(e.g., whether the power is needed at the outset of the well's life,over as much of the well's life as is feasible, or only at the tail ofthe well's life), the ambient conditions at the production site 312, theefficiency/performance of the solids and liquids separator 306 and dryer308, the conditions, including pressure, temperature and/or flow rate,specified for receipt by the pipeline 320 (often specified by thepipeline operator), and the amount of electricity desired or needed tobe produced at the production site 312 by the turboexpander 102. Incertain instances, the characteristics of the turboexpander 102(including the characteristics of the turbine wheel 104) can be selectedbased on the expected decline of the pressure of the well fluids, ratherthan the initial conditions of the fluids from the well 304. Asdiscussed above, the characteristics of the turboexpander 102, forexample, the turbine wheel 104 together with the other aerodynamicpathways through the turboexpander 102 can be designed to prioritize thepower produced by the turbine wheel 104, prioritize the pressurecharacteristics at the outlet of the turbine wheel 104 (andturboexpander housing 112), prioritize the temperature characteristicsat the outlet of the turbine wheel 104 (and housing 112) and/orprioritize or balance one or more of these characteristics.

The characteristics of the turboexpander 102 can be tuned by tuning theturbine wheel 104 design (as discussed above), as well as the design ofthe aerodynamic shapes and flow area of other aspects of theturboexpander 102 (e.g., by selecting the aerodynamic shape and area ofthe flow paths and nozzle to the turbine wheel and from the turbinewheel, through the electric rotor and stator to the outlet of theturboexpander 102). The specified pressure to which the pressure controlvalve 314 is controlled is, in turn, selected based on a number offactors, including the pressure, temperature and flow characteristics ofthe turboexpander 102, the amount of electricity desired or needed to beproduced, as well as the pressure, temperature and/or flow rate,specified for receipt by the pipeline 320. For example, in certaininstances, the pipeline 320 is configured to operate at a specifiedpressure. The turboexpander 102, which causes a pressure drop as itextracts energy from the flow, is configured to, alone or in cooperationwith one or both of the pressure control valves 314, 322, produce apressure at the inlet to the pipeline 320 (or upstream thereof, e.g., atthe outlet of the turboexpander 102) that is equal (precisely orapproximately) to the specified maximum pressure of the pipeline 320while the well 304 is producing pressure greater than the specifiedpressure of the pipeline 320. In certain instances, the pipeline 320also has a specified minimum and maximum temperature. For example, incertain instances, the specified minimum temperature can be atemperature selected to prevent freezing of condensate or hydrateformation in the gas. In certain instances, the specified maximumtemperature is selected based on the temperatures the pipe and theequipment in the pipeline can withstand or are designed (e.g., rated) towithstand. Often, the specified pressures and temperatures are specifiedby the operator of the pipeline to the operators of the production sitessupplying gas to the pipelines. The turboexpander 102, which causes atemperature drop as it extracts energy from the flow, is configured to,alone or in cooperation with one or both of the pressure control valves314, 322 (which also cause a temperature drop), maintain a temperatureat the inlet to the pipeline 320 (or upstream thereof, e.g., at theoutlet of the turbine wheel 104 and valve 322) at or below the specifiedmaximum pressure at or above the specified minimum temperature. Theturboexpander 102 can also be configured to, alone or in cooperationwith one or both of the pressure control valves 314, 322 (which alsocauses a temperature drop), maintain a temperature at the inlet to thepipeline 320 (or upstream thereof, e.g., at the outlet of the turbinewheel 104 and valve 322) at or below the specified maximum temperature.

In most instances, the turboexpander 102, alone or in cooperation withone or both of the control of valves 314, 322, can be configured tomaintain the temperature to the pipeline 320 below the specified maximumtemperature without needing a chiller, or other refrigeration orcooling, inline between the well 304 and the pipeline 320.

In certain instances, due to the conditions of the gas received by theturboexpander 102 and constraints on the energy recovery system 300, thepressure drop across the turboexpander 102 may result in a temperatureat the inlet of the pipeline 320 that is higher than the specifiedmaximum temperature of the pipeline 320. One or more chillers, or otherrefrigeration cycle, heat exchanger or cooling, can be provided in theenergy recovery system 300 or elsewhere upstream of the inlet of thepipeline 320 to further reduce the temperature to or below the specifiedmaximum temperature of the pipeline 320. But, due to the temperaturedrop produced by the energy recovery system 300, the number and/orcapacity of the chillers (or other systems) can be lower than the numberand/or capacity that would be required if no energy recovery system 300or turboexpander 102 was provided.

In certain instances, for certain inlet conditions of the process gas120 supplied to the turboexpander 102 and specified maximum pressure ofthe pipeline 320, the turboexpander 102 (e.g., aerodynamic statordefining the nozzle 154 and/or the turbine wheel 104) can be configuredto have a high isentropic efficiency (e.g., 85-90%) to prioritize powerproduction for a pressure drop across the turboexpander 102 sufficientto achieve, alone or in cooperation with one or both of the valves 314,322, a pressure at the inlet to the pipeline 320 that is at or below thespecified maximum pressure of the pipeline 320. The turboexpander 102can be configured to prioritize power production over a specified periodof the life of the well 304, such as for the majority of the life of thewell 304, the entire or a majority of the time while the well 304produces gas above a specified pressure (e.g., above the maximumspecified pressure of the pipeline 320 or another pressure above orbelow the maximum specified pressure of the pipeline 320). Prioritizingpower in this way may produce a large pressure drop across theturboexpander 102, but also cause a large temperature drop that, in someinstances, may cause the temperature to drop below the specified minimumtemperature of the pipeline 320 and/or produce freezing of condensateand hydrate formation in the turboexpander 102 and downstream. Thus, thespecified temperature conditions of the pipeline 320 can be achieved,for example, by including one or more heaters (e.g., natural gas,electric and/or other type) in the energy recovery system 300 orotherwise upstream of the inlet of the pipeline 320 to heat the flowfrom the turboexpander 102 to the specified minimum temperature of thepipeline 320.

Alternately, the turboexpander 102 (e.g., the aerodynamic statordefining the nozzle 154 and/or turbine wheel 102) can be configured tohave a lower isentropic efficiency at the received conditions of thegas, and outlet conditions described above, to extract less enthalpyfrom the gas, so that, for the same pressure drop, the outlettemperature of the turboexpander 102 is higher and the temperature atthe inlet to the pipeline 320 is above the specified minimum temperatureof the pipeline 320. The same strategy can be used to merely reduce theheating requirements upstream of the pipeline 320 as compared to aturboexpander with a turbine wheel optimized for power production,having an isentropic efficiency that may cause freezing or hydrateformation. In other words, in some instances, the aerodynamic stator andturbine wheel 104 can be configured to prioritize temperature to thepipeline 320 so that no heater/heating is required upstream ordownstream of the turboexpander 102 when operated alone or incooperation with one or both of the pressure control valves 314, 322, orso that the heater/heating is reduced from that required for aturboexpander 102 prioritized for power production. The turboexpander102 can be configured to prioritize pressure to the pipeline 320 over aspecified period of the life of the well 304, such as for the majorityof the life of the well 304, the entire or a majority of the time whilethe well 304 produces gas above a specified pressure (e.g., above themaximum specified pressure of the pipeline 320 or another pressure aboveor below the maximum specified pressure of the pipeline 320). In certaininstances, the lower isentropic efficiency can be less than 85% and, incertain instances, may be less than 80%, 75%, 70% or even 50%. Such alower isentropic efficiency can be achieved by tuning the aerodynamicstator and the turbine wheel 104 as discussed above. For example, for acertain pressure drop across the turbine wheel 104 at the same inletconditions, the turbine wheel 104 may have, as compared to a wheel withan 85-90% isentropic efficiency, additional blades, different shapedblades (e.g., less aerodynamically efficient), a greater surfaceroughness on the aerodynamic surfaces of the blades and interstitialsurfaces between the blades, and/or the blades or aspects of the wheelbeing sized to achieve a larger gap between the blade tips and thesurrounding shroud. In other words, by reducing the isentropicefficiency of the turbine wheel 104, the wheel can be configured toprioritize, for a certain pressure drop, the temperature to the inlet ofthe pipeline 320 (or upstream thereof, e.g., at the outlet of theturbine wheel 104, the turboexpander 102 or electric power generationsystem) being above a specified minimum temperature of the pipeline 320over power produced by the wheel for that same pressure drop. In someinstances, the aerodynamic stator can be adjusted to modify the velocityand direction of gas entering the turbine wheel 104. Such an adjustmentcan reduce the aerodynamic efficiency and increase the temperature tothe inlet of the pipeline 320, without affecting the pressure drop. Thesame strategy can be can be used to merely reduce the heatingrequirements over a system not so prioritized.

In yet another configuration, the turboexpander 102 (e.g., theaerodynamic stator defining the nozzle 154 and/or turbine wheel 102) canbe configured with an isentropic efficiency at the received conditionsof the gas, and outlet conditions described above, to extract aspecified enthalpy from the gas to balance power production andtemperature to the pipeline 320. The configuration is such that, whenused in combination with one or both of the pressure control valves 314,322, the pressure to the pipeline 320 is reduced to or below the maximumspecified temperature of the pipeline 320 and a specified (e.g., maximumor near maximum) amount of power is produced, while no heater/heating isrequired upstream or downstream of the turboexpander 102, or so that theheater/heating is reduced from that required for a turboexpander 102prioritized for power production. The turboexpander 102 can beconfigured to operate in this balanced state over a specified period ofthe life of the well 304, such as for the majority of the life of thewell 304, the entire or a majority of the time while the well 304produces gas above a specified pressure (e.g., above the maximumspecified pressure of the pipeline 320 or another pressure above orbelow the maximum specified pressure of the pipeline 320). As above, thelower isentropic efficiency can be less than 85% and, in certaininstances, may be less than 80%, 75%, 70% or even 50%, and can beachieved by tuning the aerodynamic stator and the turbine wheel 104.

Providing a numerical example, in certain instances, the pressure of thewell can be initially 9,000 PSIG (62.05 MPa) or higher at a temperatureof 150° F. (66° C.) and the flow is regulated down to 1,600 PSIG (11.03MPa) using the pressure control valve 314. As the well 304 ages, and thepressure declines, this 1,600 PSIG (11.03 MPa) can be maintained untilthe well's pressure drops below 1,600 PSIG (11.03 MPa). While the wellis above 1,600 PSIG (11.03 MPa), the turboexpander 102, which can beoptimized to operate at peak design efficiency under the pressure,temperature and flow conditions offered by the well 304 during thistime, operates to generate electricity, while also providing andmaintaining a further pressure drop at the inlet to the pipeline 320 (ordownstream of the turboexpander 102) to the specified pressure of thepipeline 320. The turboexpander 102 can also, or alternatively, beoptimized, alone or in cooperation with one or both of the controlvalves 314, 322, to provide a temperature at the inlet to the pipeline(or downstream of the turboexpander 102) at or below the specifiedmaximum temperature of the pipeline 320 while also maintaining thetemperature at or above the specified minimum temperature of thepipeline 320. In any instance, the hotter the well, the more energythere is available for the turboexpander 102 to extract for the same gasflow rate and minimum temperature and pressure requirements in thepipeline 320. As the well 304 pressure drops below 1,600 PSIG (11.03MPa), the efficiency of the turboexpander 102 drops off until the wellconditions can no longer operate the turboexpander 102 sufficiently.Thereafter, the first flow line 316 is shut off and flow is directedthrough only the second flow line 318, so that the turboexpander 102does not provide an additional pressure drop. In certain instances, theturboexpander 102 is configured to produce usable amounts of electricityuntil the pressure upstream approaches the pipeline's specifiedpressure. Often times, this specified pressure is 1,000 PSIG (6.89 MPa).

FIG. 4 is another example energy recovery system 400 coupled to andbetween a wellhead 402 of a well 404 (or multiple wells, in some cases)and a production pipeline 420. This second example energy recoverysystem 400 is more full featured than the example energy recovery system300 discussed with respect to FIG. 3 . For example, this second exampleenergy recovery system 400 is shown with two electric power generationsystems 450, 452, each configured like energy recovery system 350. Aswith system 300, this second example system 400 resides at theproduction site 412 (land based or offshore platform), in proximity tothe wellhead 402 and/or upstream of the production pipeline 420. Incertain instances, one or both of the electric power generation systems450, 452 are the same as the electric power generation system 100. But,as will be discussed in more detail below, the electric power generationsystems 450, 452 can have the same or different operationalcharacteristics from one another.

The system 400 includes an inlet flow line 410 coupled to the outlet ofthe wellhead 402. The well production flows from the wellhead 402 intothe flow line 410. As above, the flow line 410 includes flowconditioning equipment show in this instance as including a solids andliquid separator 406 and a dryer 408. The system 400 also is shown witha heat exchanger 416, the cool side of which is shown receiving the flowupstream from the dryer 408. Additional, different or fewer pieces andtypes of flow conditioning equipment may be provided. A pressure controlvalve 414 is shown between the wellhead 402 and the separator 406, butit could be elsewhere in the system upstream of the electric powergeneration systems 450, 452. After the dryer 408 the flow is split to acompressed natural gas (CNG) filling station line 460 leading to a CNGfilling station and a production path line 438 leading to the inlet ofthe production pipeline 420.

The line 460 to the CNG filling station includes an isolation valve 462and a pressure control valve 464. The isolation valve 462, when closed,seals the line 460 and allows the CNG filling station line 460 to beshut off so that all flow flows only to the production path line 460.The pressure control valve 464 allows the pressure to the CNG fillingstation to be regulated.

The production path line 438 has two electric power generation systems450, 452. Flow enters this portion of the system passing through the hotside of the heat exchanger 416 to collect heat from (i.e., cool) thehotter flow upstream of the dryer 408. In FIG. 4 , the flow is thensplit into a first flow line 422 that includes the electric powergeneration system 450 and a second flow line 424 that bypasses theelectric power generation system 450. The first flow line 422 and thesecond flow line 424 converge downstream of the electric powergeneration system 450, upstream of the downstream electric powergeneration system 452. In other instances, the second flow line 424 canbe omitted and the only path to the downstream electric power generationsystem 452 is through the first (upstream) electric power generationsystem 450. When provided, the second flow line 424 includes a pressurecontrol valve 426 (e.g., pressure control valve 130). The first flowline 422 includes a flow control valve 428 (e.g., flow control valve126) upstream of a flow meter 430. Thereafter, the first flow line 422includes an isolation valve 432 that can be closed to cease flow intothe first flow line 422 and the electric power generation system 450.The first flow line 422 also includes a pressure control valve 434.After the electric power generation system 450 an additional isolationvalve 436 is provided to allow the electric power generation system 450to be completely closed in and prevent backflow to the electric powergeneration system 450.

The flow is then split again into a third flow line 442 that includesthe electric power generation system 452 and a fourth flow line 444 thatbypasses the electric power generation system 452. The third flow line442 and the fourth flow line 444 converge downstream of the electricpower generation system 452, back into the production path line 438which is coupled to the inlet of the production pipeline 420. In otherinstances, the fourth flow line 444 can be omitted and the only path tothe production pipeline 420 is through the downstream electric powergeneration system 452. When provided, the fourth flow line 444 includesa pressure control valve 446 (e.g., pressure control valve 130). Thethird flow line 442 includes a flow control valve 448 (e.g., flowcontrol valve 126) upstream of a flow meter 454. Thereafter, the thirdflow line 442 includes an isolation valve 456 that can be closed tocease flow into the third flow line 442 and the electric powergeneration system 452. After the electric power generation system 452 anadditional isolation valve 458 is provided to allow the electric powergeneration system 452 to be completely closed in and prevent backflow tothe electric power generation system 452.

While the two electric power generation systems 450, 452 can beidentically configured, in certain instances, the turboexpanders and/orthe electronics of the electric power generation systems 450, 452 can bedifferently configured. The same design considerations discussed abovefor the turboexpander of electric power generation system 350 and thepressure regulation by pressure control valve 314 (FIG. 3 ) can apply tothe turboexpanders of the two electric power generation systems 450, 452and pressure control valve 414, with the further caveat that theelectric power generation system 450 can take into account the desiredor needed inlet conditions for electric power generation system 452. Forexample, the turboexpander of the upstream electric power generationsystem 450 can be configured, and the pressure control valve 414controlled, so that the conditions at the outlet of the turboexpanderare within, and preferable at or near the upper limit of, the operatingpressure range of the turboexpander of downstream electric powergeneration system 452. In certain instances, the turboexpander of theupstream electric power generation system 450 can be configured tohandle and be more efficient than the turboexpander of the downstreamelectric power generation system 452 at higher pressures, temperaturesand/or flow rates. Configuring the upstream turboexpander in this mannerallows more ready use of the declining pressures produced by the wellover its life. For example, in the embodiment of FIG. 3 , when thepressure produced by the well 304 is greater than can be handled by theturboexpander of the electric power generation system 350, the pressuresare regulated down to the efficient operating pressure range of theturboexpander, effectively delaying the conversion of the energyavailable in the flow into electric power. If the turboexpander were tobe configured to have a higher operating pressure range, the lower endof the operating pressure range would also likely increase. Thus, as thewell pressure declines, the point at which the well pressure will nolonger efficiently drive the turboexpander of the electric powergeneration system 350 would be reached sooner in the well's life. Byproviding the turboexpander of the upstream electric power generationsystem 450 configured to operate at higher pressures, for example, thesystem 400 can generate more electric power by harnessing the higherpressures with the turboexpander of the electric power generation system450. Then, as the pressures decline to the point at which the wellpressure will no longer efficiently drive the turboexpander of theelectric power generation system 450, the electric power generationsystem 450 can be isolated from the flow, and electric power generatedat lower pressures with only the turboexpander of the downstreamelectric power generation system 452. Notably, although the system 400is described herein with only two electric power generation systems,additional, such as three, four or more could be provided, each with aseparate flow path to bypass the electric power generation system andthe valves as described above, some with the separate flow path andvalves as described above, or none with the separate flow path toprovide bypass. Two or more in the set could be identically configuredor all could be differently configured, for example, with successivelylower operating ranges for each downstream electric power generationsystem. The turboexpander of the electric power generation systems canbe configured to cooperate, alone or in cooperation with one or both ofthe pressure control valves in its respective bypass line, produce apressure at the inlet to the pipeline (or upstream thereof, e.g., at theoutlet of the turboexpander) that is equal to or less than the specifiedpressure of the pipeline. The turboexpander of the electric powergeneration systems can be configured to cooperate, alone or incooperation with one or both of the pressure control valves in itsrespective bypass line, to maintain a temperature at the inlet to thepipeline (or upstream thereof, e.g., at the outlet of the turboexpander)at or below the specified pressure at or above the specified minimumtemperature and below the specified maximum temperature. In someembodiments, there may be electric power generation systems installed inparallel to each other.

In operation, flow from the wellhead 402 is regulated down in pressureto a specified pressure by the pressure regulation valve 414. The fluidthen flows through the flow conditioning system (e.g., the separator 406and dryer 408) and is cooled by cool side of the heat exchanger 416(transferring heat to the flow downstream in the system). If the CNGfilling station is operating (i.e., isolation valve 462 is open), aportion of the flow is directed to the CNG filling station line 460 andthe remainder of the flow continues on to the production path line 438.The pressure of the fluid supplied to the CNG filling station can beregulated to specified pressure by the pressure control valve 464.

In the production path line 438, the heat exchanger 416 heats the fluid(transferring heat from the flow upstream in the system). Thereafter, ifthe two isolation valves 434, 436 in the first flow line 422 are open,the flow is split into the first flow line 422 and second flow line 424.If one or both of the isolation valves 434, 436 are closed, the flowbypasses the first flow line 422 and continues to flow through thesecond flow line 424. In an instance where the flow is split between thefirst flow line 422 and the second flow line 424, the pressure controlvalve 426, pressure control valve 434 and flow control valve 428 arecontrolled to control the amount of flow that flows into the first flowline 422, and thus the turboexpander of the electric power generationsystem 450. Flow leaving the turboexpander of the electric powergeneration system 450 is recombined with the flow in the second flowline 424.

If both isolation valves 456, 458 in the third flow line 442 are open,the flow is split between the third flow line 442 and the fourth flowline 444. If one or both of the isolation valves 456, 458 in the thirdflow line 442 are closed the flow bypasses the turboexpander of theelectric power generation system 452. In an instance where the flow issplit between the third flow line 442 and the fourth flow line 444, thepressure control valve 446 and flow control valve 448 are operated tocontrol the amount of flow that flows into the third flow line 442 andthus the turboexpander of the electric power generation system 452. Flowleaving the turboexpander of the electric power generation system 452 isrecombined with the flow from the fourth flow line 444 and then proceedsto the inlet of the pipeline 420 at the specified pressure of thepipeline 420.

When the well is new and the production pressure is high, bothturboexpanders of both electric power generation systems 450, 452 can beoperated. As the well pressure declines, if the turboexpander of theelectric power generation system 450 is configured to run at a higherpressure than the turboexpander of the electric power generation system452, the pressure of flow may become too low to effectively operate theelectric power generation system 450. In this case, the isolation valves432, 436 can be closed and flow bypassed through the second flow line424 to the electric power generation system 452. The electric powergeneration system 452 can thereafter continue to operate until the wellpressure declines to a point at which the turboexpander of the electricpower generation system 452 can no longer be effectively operated.Thereafter, the isolation valves 456, 458 can be closed and flowbypassed through the fourth flow line 444 to the pipeline 420.

Providing a numerical example, in certain instances, the pressure of thewell can be initially 9,000 PSIG (62.05 MPa) or higher and the flow isregulated down to 3,600 PSIG (24.82 MPa) using the pressure controlvalve 414. As the well 404 ages, and the pressure declines, this 3,600PSIG (24.82 MPa) can be maintained until the well's pressure drops below3,600 PSIG (24.82 MPa). While the well is above 3,600 PSIG (24.82 MPa),both electric power generations systems 450, 452 can be operated togenerate electricity, while also providing and maintaining a furtherpressure drop at or upstream of the pipeline 420 to the specifiedpressure of the pipeline 420. The electric power generation systems 450,452 while also dropping the temperature at or upstream of the pipeline420 between the maximum and minimum specified temperatures of thepipeline 420. In the example, the upstream electric power generationsystem 450 is configured to depressurize the 3,600 PSIG (24.82 MPa) flowto 1,600 PSIG (11.03 MPa), and so the pressure control valve 426 is alsocontrolled to this pressure. In certain instances, the electric powergeneration system 450 is configured to have an isentropic efficiency atthese conditions of 80% or lower. Also, in this example, theturboexpander of the downstream electric power generation system 452 isconfigured to receive an inlet pressure of 1,600 PSIG (11.03 MPa). Incertain instances, the electric power generation system 452 isconfigured to have an isentropic efficiency at these conditions of 80%or lower. As the well 404 pressure drops below 3,600 PSIG (24.82 MPa),the efficiency of the turboexpander of the upstream electric powergeneration system 450 drops off until the well conditions can no longeroperate the turboexpander sufficiently. Thereafter the first flow line422 is shut off by closing the isolation valves 432, 436 and flow isonly directed through the second flow line 424. But, the second electricpower generation system 452 continues to operate with the pressurecontrol valve 426 (or optionally the pressure control valve 414)maintaining pressure to the third flow line 442 and fourth flow line 444at 1,600 PSIG (11.03 MPa). As the well 404 pressure drops below 1,600PSIG (11.03 MPa), the efficiency of the turboexpander of the downstreamelectric power generation system 452 drops off until the well conditionscan no longer operate the turboexpander sufficiently. Thereafter, thethird flow line 442 is shut off by closing isolation valves 456, 458 andflow is directed through only the fourth flow line 444, so that theturboexpander does not provide an additional pressure drop. In certaininstances, the turboexpander of the downstream electric power generationsystem 452 is configured to produce usable amounts of electricity untilthe pressure upstream approaches the pipeline's specified pressure.Often times, this specified pressure is 1000 PSIG (6.89 MPa).

In the foregoing specification, a detailed description has been givenwith reference to specific exemplary embodiments. It will, however, beevident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the disclosure asset forth in the claims.

What is claimed is:
 1. A system for cooling flow from a gas well priorto a production pipeline, comprising: an inlet flow line coupled to awellhead of the gas well to receive gas produced from the gas well; anda flow line coupled to the inlet flow line to receive the gas andcoupled to the production pipeline to direct the received gas away froma production site, the flow line residing at the production site andcomprising an electric power generation system, the electric powergeneration system comprising: a turbine wheel configured to receive thegas and rotate in response to expansion of the gas flowing into an inletof the turbine wheel and out of an outlet of the turbine wheel, a nozzleconfigured to direct gas into the inlet of the turbine wheel, anelectric rotor coupled to the turbine wheel and configured to rotatewith the turbine wheel, and a stationary electric stator, the electricrotor and electric stator defining an electric generator configured togenerate current upon rotation of the electric rotor within the electricstator, and the turbine wheel configured to reduce the temperature ofthe received gas at an inlet to the production pipeline to at least aspecified temperature associated with the production pipeline.
 2. Thesystem of claim 1, where the pressure of the flow from the gas well isexpected to decline from an initial pressure over the operating life ofthe well, and where the nozzle and the turbine wheel characteristics areselected to maintain a temperature of the received gas at an inlet tothe production pipeline to be above the specified temperature while thewell is producing gas above a specified maximum pressure associated withthe production pipeline.
 3. The system of claim 1, where the specifiedtemperature is a specified maximum temperature for gas supplied to theproduction pipeline.
 4. The system of claim 1, where the nozzle and theturbine wheel are configured to reduce the temperature of the receivedgas to 38° C. or lower.
 5. The system of claim 4, where the turbine isconfigured to reduce the temperature of the received gas whilemaintaining the temperature above a hydrate formation temperature of thegas at the outlet of the turbine wheel.
 6. The system of claim 5, wherethere is no heater between the turbine wheel and the productionpipeline.
 7. The system of claim 1, comprising a second flow linecoupled to the inlet flow line to receive the gas and provide analternate flow path for the gas around the first mentioned flow line,the second flow line comprising a pressure control valve, and where thefirst mentioned flow line and the second flow line are coupleddownstream of the electric power generation system to recombine flowfrom the first mentioned flow line and the second flow line.
 8. Thesystem of claim 7, where the nozzle and the turbine wheel are configuredto, in cooperation with the pressure control valve in the second flowline, maintain a temperature of the received gas at an inlet to theproduction pipeline to be above a specified minimum temperatureassociated with the production pipeline while the well is producing gasabove a specified maximum pressure associated with the productionpipeline.
 9. The system of claim 8, where the nozzle and turbine wheelare configured to, in cooperation with the pressure control valve in thesecond flow line, maintain a pressure of the received gas at the inletto the production pipeline to be below the specified maximum pressureassociated with the production pipeline.
 10. The system of claim 8,where the nozzle and the turbine wheel characteristics are selected tomaximize the amount of power produced by the electric power generationsystem while, in cooperation with the pressure control valve in thesecond flow line, maintaining a temperature of the received gas at aninlet to the production pipeline above the specified minimum temperaturewhile the well is producing gas above a specified maximum pressureassociated with the production pipeline.
 11. The system of claim 1,comprising a hermetically sealed housing enclosing the turbine wheel,the electric rotor and the electric stator and hermetically sealedinline in the first mentioned flow line so that received flow flowsthrough the turbine and over the electric stator.
 12. The system ofclaim 1, where the electric rotor comprises a permanent magnet rotor.13. The system of claim 1, comprising a flow control valve in the flowline upstream of the electric power generation system.
 14. A method ofconditioning a flow from a gas well for a production pipeline,comprising: receiving flow from the gas well at a flow line, the flowline comprising an electric power generation system residing on aproduction site of the well and comprising: a turbine wheel configuredto receive the gas and rotate in response to expansion of the gasflowing into an inlet of the turbine wheel and out of an outlet of theturbine wheel, a nozzle configured to direct gas to the inlet of theturbine wheel, an electric rotor coupled to the turbine wheel andconfigured to rotate with the turbine wheel, and a stationary electricstator, the electric rotor and electric stator defining an electricgenerator configured to generate current upon rotation of the electricrotor within the electric stator; and flowing a portion of the flow fromthe gas well through the flow line and the electric power generationsystem and, with the turbine, reducing the temperature of the gas, at aninlet to the production pipeline, to at least a specified temperatureassociated with the production pipeline.
 15. The method of claim 14,where the specified temperature is a maximum specified temperature forgas supplied to the production pipeline.
 16. The method of claim 14,comprising maintaining a minimum temperature of the gas above a hydrateformation temperature of the gas at the outlet of the flow line.
 17. Themethod of claim 14, comprising receiving flow from the gas well at asecond flow line, flowing a portion of the flow from the gas wellthrough the second flow line and a portion of the flow from the gas wellthrough the first mentioned flow line and then combining the portionsdownstream of the electric power generation system.
 18. The method ofclaim 17, where flowing a portion of the flow through the firstmentioned flow line and a portion of the flow through the second flowline comprises controlling a flow control valve in the first mentionedflow line and a pressure control valve in the second flow line to reducea temperature of the recombined flow to 38° C. or lower.
 19. The methodof claim 18, comprising controlling the pressure control valve in thesecond flow line to maintain a temperature of the received gas at aninlet to the production pipeline to be above a specified minimumtemperature while the well is producing gas above a specified maximumpressure associated with the production pipeline.
 20. The method ofclaim 19, comprising controlling the pressure control valve in thesecond flow line to maintain the pressure of the received gas at theinlets to production pipeline to be above the specified maximum pressureassociated with the production pipeline.
 21. The method of claim 19,where the nozzle and the turbine wheel characteristics are selected tomaximize the amount of power produced by the electric power generationsystem while, in cooperation with the pressure control valve in thesecond flow line, maintaining a temperature of the received gas at aninlet to the production pipeline above the specified minimum temperaturewhile the well is producing gas above a specified maximum pressureassociated with the production pipeline.
 22. The method of claim 14,where the electric power generation system comprises a hermeticallysealed housing enclosing the turbine wheel, the electric stator and theelectric rotor and hermetically sealed to the remainder of the flow lineand where flowing a portion of the flow from the gas well through theflow line and the electric power generation system comprises flowing theflow around the electric stator.
 23. A system, comprising: a flow pathfrom a well to a production pipeline comprising a nozzle and a turbinewheel coupled to a generator residing on a production site of the well;and the nozzle and the turbine wheel configured to reduce thetemperature of gas received through the flow path to at least aspecified temperature associated with the pipeline.
 24. The system ofclaim 23, where the turbine wheel and generator reside in a hermetichousing defining a portion of the flow path.
 25. The system of claim 23,where the generator comprises a permanent magnet rotor.
 26. The systemof claim 23, where the specified temperature is 38° C.
 27. The system ofclaim 23, comprising a second flow path between the well and thepipeline, where the first mentioned flow path and second flow pathconverge upstream of the pipeline.
 28. The system of claim 27, where thesecond flow path comprises a pressure control valve, and where thenozzle and turbine wheel are configured to, in cooperation with thepressure control valve, reduce the pressure of the gas received from thewell to below a specified maximum pressure associated with theproduction pipeline.
 29. The system of claim 28, where the specifiedtemperature is a maximum specified temperature associated with thepipeline.
 30. The system of claim 29, where the nozzle and turbine wheelare configured to maximize power production by the generator.